Object initializer surprise.

thingthangthung.cs

void Main()
{
  var t = new Thing(new Thang { Thung = "lol" })
  {
    Thang = { Thung = "OMG" } 
  };
	
  t.Dump();
}

class Thing
{
  private readonly Thang _thang;

  public Thing(Thang thang)
  {
    _thang = thang;
  }

  public Thang Thang
  {
    get { return _thang; }
  }
}

class Thang
{
  public string Thung { get; set; }
}